1. Field of the Invention
This invention relates to investment casting molds and in particular to an alumina mold made from a silica-bonded alumina investment casting mold.
2. Description of the Prior Art
Investment casting of superalloy materials and directionally solidified eutectic materials for making aircraft engine turbine blades is currently practiced in silica-bonded alumina molds. The presence of the silica in the mold limits the casting temperature and, therefore, the alloys which can be successfully cast. In addition, silica can react with the superalloy metal cast in contact therewith thereby causing surface defects. Precision casting is limited because of the defective surfaces and/or oversize parts must be cast and then machined to size in order to remove the surface defects.
An all alumina mold would enable one to cast at higher temperatures and to substantially reduce defects in the casting, particularly in the surface areas.
Therefore, it is an object of this invention to provide a new and improved alumina mold for the investment casting of superalloy materials and directionally solidified materials which overcomes the deficiencies of the prior art.
Another object of this invention is to provide a new and improved alumina mold wherein the microstructure is indicative of alumina molds made from silica-bonded alumina molds.
Other objects of this invention will, in part, be obvious and will, in part, appear hereinafter.